The present invention relates to torque sensor, wire harness, electric power steering assembly and terminal holder.
Conventionally, an electric power steering assembly employs a torque sensor for detecting a steering torque. A torque applied to a steering shaft is detected by the torque sensor so that a steering assist force can be controlled based on the torque thus detected.
The torque sensor detects the torque as follows. A cylindrical gear portion is provided to each of an input shaft and an output shaft which are interconnected by means of a torsion bar and which constitute a steering shaft, in a portion where the steering shaft is surrounded by a sensor coil. The gear portions are so provided as to oppose to each other. A torque applied to the steering shaft causes the gear portions to be angularly displaced relative to each other, while the relative angular displacement is detected by way of a variation of impedance produced in the sensor coil.
Such an electrical power steering assembly includes: the steering shaft; the sensor coil disposed on an outer periphery of the steering shaft so as to detect the torque applied to the steering shaft; a plurality of lead pins projecting from an outer periphery of the sensor coil; a control unit for detecting a steering torque based on a variation of the impedance produced in the sensor coil and for controlling an electric motor for steering assist depending on the detected torque; and a control board constituting the control unit.
The torque sensor for use in the electric power steering assembly includes one wherein the control board is disposed in close vicinity of the sensor coil and the lead pins are directly connected with the control board without using the wire harness (see, for example, Japanese Unexamined Patent Publication No.2003-11833).
This torque sensor has the lead pins inserted in through-holes formed in a substrate portion constituting the control board and connected with the substrate portion by means of solder for electrical conductivity.
In an arrangement wherein the wire harness is used for connecting the lead pins with the control board of a control unit spaced away from the sensor coil, however, each of the lead wires of the wire harness must be connected with each of the lead pins and soldered thereto. This results in a low efficiency of a wiring operation.
In order to increase the efficiency of the wiring operation when the wire harness is connected with the lead pins, it can be contemplated to provide a connection terminal and a terminal holder to permit the wire harness to be mounted to the lead pins in one step. The connection terminal includes: a sleeve through which the lead pin can be inserted, and a connection portion to which the lead wire of the wire harness is connected. The terminal holder is adapted for integral retention of the sleeves.
However, a dip soldering operation of dipping a tip of the lead pin with the sleeve mounted therearound into a high-temperature solder bath is performed for ensuring the connection between the lead pin and the sleeve. During the soldering operation, the connection portions may be inadvertently bent to bring the connection terminals into contact with each other. That is, this approach is somewhat decreased in the reliability of preventing the contact between the connection terminals although the efficiency of the wiring operation is increased.